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Definition

An arrhythmia is an abnormal heart rhythm. This could be a heart rhythm that is too fast, too slow, or just irregular. When defining arrhythmias they are usually divided into two major categories:

1) Bradyarrhythmias - these are any type of slow heart rhythm. This can involve an abnormality of the sinus node, the atrial tissue surrounding the sinus node, the AV node, or in the His-Purkinje system (see Electrical Function of the Heart).

2) Tachyarrhythmias - these are any type of fast heart rhythm. This group can be divided into two major categories:

a) Supraventricular Tachycardias (SVT) - these are arrhythmias which either originate from the upper chambers of the heart (atria) or involve extra electrical pathways that connect the upper and lower chambers of the heart. Examples are atrial fibrillation, atrial tachycardia, AV node reentry tachycardia, and AV reentry tachycardia.
b) Ventricular Tachyarrhythmias - these are arrhythmias that originate from the lower chambers of the heart (ventricles). There are two main types of ventricular tachyarrhythmias - ventricular tachycardia and ventricular fibrillation.

Some arrhythmias can occur when there is a primary abnormality of the muscle of the heart (ie. atrial fibrillation, atrial tachycardia, ventricular tachycardia) or when the correct electrical situation occurs involving an extra electrical pathway present in the heart (i.e. AV node reentry tachycardia & AV reentry tachycardia).

The treatment of each arrhythmia depends on many factors including the patient's age, other illnesses that might be present, the symptoms present during the arrhythmia, medications the patient is taking, and the frequency with which the arrhythmias occurs (to name only a few). Your electrophysiologist will decide, along with you and your cardiologist, which treatment might be best for you.

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Sinus Node Dysfunction

Scarring in the region of the sinus node can cause abnormalities in the initiation of an electrical impulse (intrinsic sinus node disease) or in the conduction of the impulse from the sinus node through the atrial tissue surrounding the node (extrinsic sinus node disease). The scarring can be caused from long-standing hypertension (high blood pressure), myocardial infarctions (heart attacks), or from viral infections of the heart muscle (myocarditis). Some medications, such as beta-blockers and calcium channel blockers, can worsen sinus node dysfunction. These medications might need to be discontinued or have their doses decreased to prevent worsening of the sinus node dysfunction. Fast heart rhythms, such as atrial fibrillation, atrial flutter, and atrial tachycardia, are associated with sinus node dysfunction. It is not uncommon to have both slow and fast heart rhythms in the same patient. This syndrome is referred to as tachy-brady syndrome or sick sinus syndrome. The implantation of a pacemaker is often necessary to prevent symptomatic bradycardia and enable the use of medications to limit the number of fast heart arrhythmias that occur (see the Pacemakers section).

If the sinus node dysfunction is associated with symptoms such as lightheadedness, dizziness, extreme fatigue, shortness of breath with exertion, or passing out (syncope) then a pacemaker will likely need to be implanted. The correlation of these symptoms with a slow heart rhythm is often done using a Holter monitor or a loop recorder (see the Holter Monitors / Event Monitors / Loop Recorders section). Sometimes more vague symptoms of weakness or fatigue and inability to walk long distances can be attributed to a slow heart rhythm. An exercise stress test or an electrophysiology study (see the Electrophysiology Studies section) are sometimes needed prior to recommending definitive therapy with a pacemaker for patients with these symptoms.

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AV Node Dysfunction

Just as scarring can occur in the region of the sinus node, it can also occur around the area of the AV node. Some medications, such as beta-blockers and calcium channel blockers, can worsen AV node dysfunction. These medications might need to be discontinued or have their doses decreased to prevent worsening of the AV node dysfunction. Abnormalities in AV node conduction can prevent impulses initiated by the sinus node from reaching the ventricles. This is called heart block. There are varying degrees of heart block, some of which do not typically require treatment, and some of which are serious and require a permanent pacemaker (see the Pacemakers section). For example, if no impulses initiated from the sinus node ever reach the ventricles then this is referred to as complete heart block (or third degree heart block). Typically, in complete heart block, a separate stable rhythm originates from the region just below the AV node (referred to as an escape rhythm) which prevents total electrical standstill in the ventricles. Symptoms of complete heart block range from fatigue and weakness to dizziness and passing out to cardiac arrest and death. If only every other impulse originating in the sinus node reaches the ventricles then this is referred to as 2:1 (2 to 1) heart block. If only 2 of every 3 impulses reaches the ventricle then this is referred to as 3:2 (3 to 2) heart block. Each individual patient with heart block needs to be fully assessed to determine what (if any) treatment might be needed for their form of heart block.

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His-Purkinje System Dysfunction

Scarring can also occur in and around the electrical conduction system present below the AV node, called the His-Purkinje conduction system. Abnormalities in the His-Purkinje conduction system can prevent impulses initiated by the sinus node from reaching the ventricles. This is called heart block (more specifically, infrahisian heart block). When heart block occurs because of a diseased His-Purkinje conduction system a separate rhythm (escape rhythm) can originate from somewhere in the ventricles. However, an escape rhythm from the ventricles is inherently less stable than one from just below the AV node (as in AV nodal heart block) and can more frequently lead to passing out or death. All patients with proven infrahisian heart block need to have a permanent pacemaker implanted. Typically, the location of heart block is elucidated during an electrophysiology study (see the Electrophysiology Studies section).

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Supraventricular Tachyarrhythmias (SVT)

These are arrhythmias which either originate from the upper chambers of the heart (atria) or involve extra electrical pathways that connect the upper and lower chambers of the heart.  There are many different forms of SVT, they include:

  • Atrial Fibrillation - Atrial fibrillation (AF) is a disorganized rhythm in the upper chambers of the heart (atria). The rate at which the atria fibrillate is very rapid (the equivalent of 600-800 beats per minute). Intermittently, one of these impulses travels through the AV node and into the ventricles. This leads to the typical irregularly irregular pulse in patients with atrial fibrillation. The rate at which these impulses travel through the AV node and into the ventricles is highly variable and depends on many different factors including the amount of scarring around the AV node, medications, and the patient's activity. The rate can sometimes be rapid which can lead to symptoms of palpitations, shortness of breath, dizziness, and lightheadedness. Some patients might have no symptoms at all when in atrial fibrillation and it is sometimes discovered at a routine physical exam.
  • Atrial Flutter - Atrial flutter is a more organized arrhythmia that occurs in the right atrium. The typical rate of atrial flutter in the atria is 300 beats per minute. These impulses typically travel through the AV node in a regular fashion. For example, if every other atrial flutter beat travels through the AV node to the ventricles, the heart rate is 150 beats per minute (300 divided by 2 = 150). If every 3rd beat gets through the AV node, the heart rate is 100 beats per minute. Atrial flutter can be associated with symptoms of palpitations, shortness of breath, dizziness, and lightheadedness but patients can also be asymptomatic.
  • Atrial Tachycardia - Atrial tachycardia is a regular arrhythmia that can arise from any location in either atrium. The rate of an atrial tachycardia is variable and can range from ~ 100 beats per minute to 300 beats per minute. The atrial tachycardia impulses typically travel through the AV node in a regular fashion. Either every 2nd or 3rd or 4th atrial tachycardia beat is conducted through the AV node to the ventricles. Sometimes the conduction of the atrial tachycardia through the AV node varies and the resulting pulse can be sensed as irregular. Atrial tachycardia can be associated with symptoms of palpitations, shortness of breath, dizziness, and lightheadedness but patients can also be asymptomatic.
  • AV Node Reentry Tachycardia - AV node reentry tachycardia (AVNRT) is a form of SVT which utilizes an extra electrical pathway present in (or near) the AV node. Typically, when an impulse travels from the atria to the ventricles, it travels through the normal electrical pathway of the AV node (called the fast pathway). If a premature beat from the upper or lower chambers of the heart (APC and VPC, respectively) occurs and the proper electrical situation exists, the impulse can travel down the extra electrical pathway (called the slow pathway) and back up the fast pathway. If this continues (down the slow pathway and up the fast pathway) then tachycardia ensues. The rate of AVNRT is variable ranging from ~ 120 beats per minute to 240 beats per minute. Symptoms include palpitations, shortness of breath, dizziness, and lightheadedness. Passing out (syncope) is rare. There is no known association with strokes or myocardial infarction. AVNRT can be persistent and require a visit to the emergency room for termination (usually with an intravenous medication called adenosine) or can be paroxysmal. Sometimes, bearing down (as if straining) can terminate the tachycardia
  • AV Reentry Tachycardia (WPW) - AV reentry tachycardia (AVRT) is a form of SVT that utilizes an extra electrical pathway (called an accessory pathway) which connects the atria and the ventricles. These pathways can be located anywhere around either of the two valve rings (the mitral valve ring connects the left atrium and left ventricle and the tricuspid valve ring connects the right atrium and right ventricle). The most common location is around the mitral valve ring. Some accessory pathways can conduct only from the ventricle up to the atrium in which case they are referred to as concealed accessory pathways. Other accessory pathways can conduct both from the ventricle to the atrium and from the atrium back down to the ventricle. Only accessory pathways that conduct from the atrium to the ventricle can be recognized on a routine electrocardiogram (ECG). Typically, your physician can surmise the approximate location of the accessory pathway by examining your ECG.

All of the above forms of SVT can be treated in many different ways.  Some do not require any treatment, others can be treated with medications, and others may need to be treated with radiofrequency ablation (see Catheter Ablation).  You will need to discuss the best treatment option with your electrophysiologist and cardiologist.

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Ventricular Tachyarrhythmias

These are arrhythmias that originate from the lower chambers of the heart. They fall into two major categories: Ventricular Tachycardia and Ventricular Fibrillation.
  • Ventricular Tachycardia - Monomorphic ventricular tachycardia (MVT) is a regular arrhythmia originating from the lower chambers (ventricles) of the heart. MVT can be asymptomatic or can cause palpitations, lightheadedness or dizziness, syncope (passing out), or even death. The rate of MVT can range from 100 beats per minute to in excess of 280 beats per minute. Sustained MVT is never a "normal" occurrence and always needs to be evaluated and treated.
  • Ventricular Fibrillation - Ventricular fibrillation (VF) is a rapid and chaotic rhythm of the ventricles which, if not corrected rapidly (by cardioversion), universally leads to death. During VF, the ventricles are unable to pump adequate amounts of blood to the rest of the body which results in loss of consciousness in anyone with this arrhythmia. Primary VF is usually caused by ischemia (not enough blood flow to the muscle of the heart). VF can be seen in patients who initially had monomorphic VT or polymorphic VT as their initial arrhythmia which over time changed into (or degenerated into) VF. There are rare disorders of the heart muscle involving ion channels (potassium and sodium) which can be inherited that can lead to VF. Therapy involves reversal of the underlying cause for the VF as well as medications and possibly an internal cardioverter defibrillator (ICD).
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